when i start moving and stop moving mr rear end rotates uo and down its a 2000 ranger 4x4

 

It'snormal torotate a little,but check the U-bolts that hold the rear end to the leaf springs.

 

Small amount of up and down motion is normal as well as very slight up pitch in the pinion angle during take off (particularly full or near full throttle launches). If you seem to be experiencing a lot check your springs for a cracked leaf..............